1. Field of the Invention
This invention relates to the structure of a double inlet wheel of a centrifugal blower with forward curved blades used in devices such as air conditioners, ventilators, exhaust systems and instrument cooling units (referred to hereafter as wheel), and to the method of manufacturing this wheel. This wheel has the advantages of greater lightweightness, quieter operation and higher efficiency. This application is described insofar as it applies to the case of a double inlet wheel, but it may be applied also to the case of a single inlet wheel.
2. Prior Art
Conventional wheels may be broadly divided into three types according to their construction and the materials of which they are made. These types will hereinafter be referred to as type A wheel, type B wheel and type C wheel. The type A wheel consists of a large number of individual blades, a pair of end rings and a center disk. An example of this type is disclosed in U.S. Pat. No. 2,852, 182. The type B wheel comprises a continuous strip blade which forms a cylindrical body, a pair of end rings, and a center disk. An example of this type is disclosed in U.S. Pat. No. 3,335,482. In both type A and type B wheels, all parts are made of metal plates, the cross-sectional form of the blades being that of a curved flat plate rather than an airfoil shape. The operation of the wheel is therefore noisy, and it is not very efficient. In the type B wheel, the blades are fashioned from a single metal strip, hence there are limitations on the number of blades and their arc length which makes it difficult to obtain the desired air volume and pressure. However, as the construction involves only two parts, productivity is high and operating precision after assembly is high. Type C is made in a one-piece construction by injection molding of a plastic material, the cross-sectional form of the blades being that of an airfoil. No previous applications have been found in the literature regarding this type. Of the three types, type C is the quietest in operation and it has the highest efficiency, but as the strength of the material is lower than that of metal, it is not possible to manufacture a wheel of large diameter. It is also subject to creep and deformation with temperature rise, so the places in which it can be operated are limited.
All three types have their respective advantages and disadvantages, hence there was no blower which was completely satisfactory in all points. The type of wheel was therefore chosen depending on the place where it was to be operated and on the running conditions.
In recent years, more blowers are coming to be installed near by living spaces and working spaces, and a need has emerged for higher efficiency with less noise. At the same time there is a need for greater compactness, which means the blower must be operated at even higher speeds. Blower wheels therefore have to withstand high speeds, be rigid and have a good dynamic balance. In particular, in the case of air conditioning or ventilation systems, more units are being installed in or suspended from ceilings so as to enable more effective use of floor space. This creates a greater need for blowers to be more lightweight and quieter in operation, however these requirements cannot be met by the aforementioned conventional wheel structures and manufacturing methods.